Repair of torn soft tissue has changed dramatically over recent years. Generally, techniques for repairing soft tissue tears involve reattaching the torn tissue back to the bone from which it is avulsed. Typically, suture material is used to tie the tissue directly back to bone to facilitate healing of the tissue. Open techniques for reattaching soft tissue to bone often require large incisions, resulting in long periods of immobilization and rehabilitation for the affected tissues as well as increased morbidity resulting from the lengthy surgery.
More recently, closed techniques, and fixation devices for use in closed techniques, have been developed to relieve some of the disadvantages resulting from the use of open techniques to attach soft tissues to bone. Suture anchors are one type of device known for use in attaching soft tissue to bone in closed surgical procedures. Examples of such anchors and their use may be found in U.S. Pat. Nos. 4,898,156; 4,899,743; 5,207,679; 5,217,486; 5,417,713; and 5,522,845. Generally, a suture anchor is inserted into a preformed bore in a bone where the suture anchor fixes to an internal portion of the bone. A length of suture thread, either pre-threaded in the anchor or threaded through an eyelet in the anchor after insertion, is used to tie the injured tissue into place so that healing may occur.
In some instances, it may be preferable to attach the soft tissue to bone without the need to tie the soft tissue with suture thread. One type of device that has been developed to meet this need is the tissue tack. Tissue tacks, such as those shown in U.S. Pat. Nos. 4,976,715; 5,261,914; 5,380,334; and 5,601,558, generally have an elongate portion and a head portion. The elongate portion is passed through a hole in the tissue and into a preformed bore in a bone. The head portion has a larger diameter than the hole in the tissue and thus serves to secure the tissue to the bone when the elongate portion is inserted into the bore. Often, tissue tack devices are constructed from bioabsorbable materials so that further surgery is not needed to remove the tack when tissue mending is complete.
Generally, bone fixation elements on tissue tacks such as those disclosed in the U.S. patents listed above are limited to circumferential ridges disposed on the elongate portion of the tack which form a friction fit within the bore in the bone. While this form of bone fixation may be sufficient for patients with very high quality bone, it is insufficient for many other patients, especially older patients, who may have poor quality bone, osteopenic bone or bone that has been weakened by disuse due to pain. Accordingly, there remains a need for tissue tacks having improved bone fixation elements so that such tacks may be used with a wider variety of patients who could benefit from the use of tissue tacks.